1. Field of the Invention
This invention relates to a process for the preparation of substituted diphenylalkanes and is more particularly concerned with an improved synthesis of di(aminophenyl)alkanes.
2. Description of the Prior Art
Various methods are known for the preparation of 2,2-bis(4-aminophenyl)propane and like bis(aminophenyl)alkanes. Illustratively, the former has been prepared by the condensation of acetone and aniline hydrochloride; see U.S. Pat. No. 3,670,024. An earlier process for the same compound involved the reaction of acetone and aniline under pressure in the presence of hydrochloric acid to yield the diamine in question in low yield; see U.S. Pat. No. 2,794,822. 2,2-Bis(4-aminophenyl)propane has also been prepared by direct amination of bisphenol A (see U.S. Pat. No. 3,860,650) and, as a by-product in low yield, by the reaction of bisphenol A with aniline (see U.S. Pat. No. 3,418,371). The main product of the latter reaction is 2-(4-hydroxyphenyl)-2-(4-aminophenyl)propane.
I have now found that 2,2-bis(4-aminophenyl)propane and related compounds can be obtained in high yield by an improved process which will be described below.
In my copending application Ser. No. 898,646 filed Apr. 21, 1978 and now U.S. Pat. No. 4,177,211 there is described a process for the preparation of 2,2-bis(4'-aminophenyl)propane and related compounds by reacting the corresponding 2,2-bis-(2,4-dialkoxyphenyl)alkanes with an aniline acid addition salt at elevated temperature. The process of the present invention represents an alternative route to the production of 2,2-bis(4'-aminophenyl)propane and related compounds from readily available, inexpensive starting materials via intermediates which are clearly different from those employed in the aforesaid copending application.